The phenothiazines, a class of drugs widely used for childhood mental disorders, inhibit growth hormone (GH) secretion by an action on monoaminergic transmission in the hypothalamus. This action might cause growth failure during chronic administration. A nonstressful frequent sampling method will be utilized with rats to determine the effect of phenothiazines on the endogenous secretory rhythm of growth hormone. The completeness of inhibition, dose-response relationship and relative activities of perphenazine, chlorpromazine and thioridazine will be determined. The effect of perphenazine on growth in length and weight of immature rats will be studied. In experiments to determine the impact of phenothiazines on the growth process, immature rats will be given perphenazine or saline and growth in weight, body length and tail length determined. Pair feeding will be employed to eliminate nutritional differences. The project is expected to provide the basic information on the effect of phenothiazines on GH secretion and growth needed to plan clinical studies in human children.